There's no doubt in my mind that parking lot usage is down significantly. I was in Wisconsin at the end of August and drove by during the Saturday night game against San Diego that was nearly sold out and the parking lots looked similar to those photos above. Maybe for Cubs games it is higher, I don't know, but it used to be a common thing for the lots to completely fill up, requiring them to park cars along the road to squeeze everybody in.
Even the last time I was there in 2018 for the NLCS I wasn't able to purchase parking because I bought tickets at the last second and the lots were sold out.
I'm sure the calculation for the Brewers is pretty straightforward -- they make more money by charging more and it's also better for traffic and the environment.